The present invention relates in general to cryptography, and in particular to providing secure access to a secret.
In this era of digital entertainment, content that is stored as a digital file can easily be copied without any loss of quality. The movie and music industries lose vast amounts of money due to illegal copying and sharing of this content. Efforts have been made to provide digital rights management (DRM) to deliver content to a consumer without also allowing the consumer to copy the content. High-Bandwidth Digital Content Protection (HDCP) is a DRM standard developed to control digital audio and video content as it travels across, for example, Digital Visual Interface (DVI) or High Definition Multimedia Interface (HDMI) connections (e.g., from a DVD player to a display device).
As part of HDCP or other content protection protocols, a content data stream is to be encrypted any time it travels between devices. For example, the data stream from a content medium, such as High Definition (HD) DVD and Blu-ray Discs, is encrypted. However, the data stream typically requires processing, e.g. by a graphics processing unit (GPU) within a DVD player, which must be done with the unencrypted data. Thus, the GPU must decrypt, process, and then re-encrypt the data stream before sending it to a display.
The display key used by the GPU in the re-encryption process needs to be kept a secret, or else all content may be compromised. Additionally, the HDCP standard specifies that if the re-encryption process performed by a particular GPU is cracked, then only that GPU is compromised. In other words, the information obtained in the cracking of the re-encryption process for one GPU should not be useful for cracking the re-encryption process of another GPU.
Therefore it is desirable to provide methods, devices, and systems of keeping the display key secret while allowing use of the display key in a re-encryption process. It is further desirable to ensure that the compromise of one secret display key does not result in the compromise of all display keys.